The present invention relates generally to microfluidic analysis systems, and more specifically to micro-Total Analysis Systems xcexc-TAS), for performing liquid phase analysis at a miniaturized level.
Recent developments in the field of micro-Total Analysis Systems (xcexc-TAS) have led to systems that perform chemical reactions, separation and detection at a miniaturized level on a single microchip [see, for example Harrison, D. J. ; Fluri, K.; Fan, Z.; Effenhauser, C.S.; and Manz, A., Science 1993, 261, 895-897. Harrison, D. J.; and van den Berg, E.; Eds., Micro Total Analysis Systems ""98, Proceedings of the xcexcTAS ""98 Workshop (Kluwer: Dordrecht, 1998), Coyler, C. L.; Tang, T.; Chiem, N.; and Harrison, D. J., Electrophoresis 1997, 18 1733-1741].
Most prior art microfluidic devices are based on conventional open tubular flow designs and solution phase reagents. While the functionality of these devices has continued to increase, one key feature that is presently lacking in these prior art devices is the ability to effectively incorporate on-chip packed reactor beds, for introduction of packing materials with immobilized reagents or stationary phases. While a few attempts have been made to employ packed reactor beds in some prior art designs, the difficulty of packing portions of a complex microfluidic manifold with packing material (such as microscopic beads) has so far hindered the effective utilization of these reagent deliver vehicles within microfluidic devices. (The difficulty of packing has been well recognized by practitioners in the field [see, for example, Ericson, C; Holm, J.; Ericson, T.; and Hjertxc3xa9n, S., Analytical Chemistry.)
In one prior art example, a packed bed chromatographic device with a bead trapping frit was fabricated in a silicon substrate [Oevirk, G., Verpoorte, E., Manz, A., Grasserbauer, M., and Widmer, H. M. Analytical Methods and Instrumentation 1995, 2, 74-82]. However, the packing material in this prior art design could not be readily packed or exchanged, thus limiting its utility.
Several authors have also described the difficulties associated with reproducibly fabricating frits for retaining packing material in conventional capillaries [Boughtflower, R. J.; Underwood, T.; Patterson, C. J. Chromatographia 1995, 40, 329-335. Van den Bosch, S. E.; Heernstra, S.; Kraak, J. C.; Poppe, H. J. Chromatogr. A 1996,755, 165-177. Colon, L. A.; Reynolds, K. J.; Alicea-Maldonado, K.; Fermier, A. M. Electrophoresis 1997, 18, 2162-2174. Majors, R. E. LC CC 1998, 16, 96-110.]. The frits used in conventional systems are prepared using time and labor intensive procedures, the most commonly used method involving the use of pure silica gel, wetted down with aqueous sodium silicate. The frit is made by first tapping a capillary end into a paste made from silica and aqueous sodium silicate. The resulting plug of silica is then heated to make a frit.
Furthermore, using frits produced by prior art methods of construction often leads to the formation of undesirable bubbles. Altria, K. D.; Smith, N. W.; and Turnbull, C. H., Chromatographia, 46 (1997) 644. Majors, R. E., LC-GC, 16 (1998) 96. ]Bubbles cause discontinuity within a column, hindering solution flow and ultimately preventing separation from occurring. The bubbles are thought to arise from a change in electroosmotic flow (EOF) velocity caused by moving from a bead trapping frit into an open capillary. The formation of bubbles, which have been observed to increase at higher voltages, also limits the amount of voltage that can be applied across the capillary, thereby limiting column lengthy, separation efficiency, and speed of analysis.
Developing a functional on-chip packed reactor bed design which overcomes the limitations in the prior art would significantly enhance the range of the microfluidic toolbox and extend the number of applications of such devices.
Generally, the present invention provides an on-chip packed reactor bed design using one or more weir structures that allow for an effective exchange of packing materials (beads for example) at a miniaturized level. The present invention extends the function of microfluidic analysis systems to new applications. For example, the packed reactor bed formed according to the present invention allows on-chip solid phase extraction (SPE) and on-chip capillary electrochromatography (CEC), as explained in detail further below. The design can be further extended to include, for example, integrated packed bed immuni- or enzyme reactors.
More specifically, the present invention provides:
A microfluidic analysis system, comprising:
a) a substantially planar substrate having an upper surface;
b) at least one main channel formed into said upper surface, said main channel having first and second ends and a defined direction of flow in use;
c) a cover plate arranged over said planar substrate, said cover plate closing off said channel from above; and
d) a first weir formed across said main channel and between said first and second ends of said channel, said first weir providing at least one flow gap to allow, in use, at least some fluid to flow past said first weir while trapping packing material having constituent particles that are generally larger than said flow gap.
The microfluidic analysis system may further comprise at least one side channel formed into said planar substrate, said side channel being connected at a first end to said main channel at a location upstream from said first weir, and at a second end to a reservoir, said side channel providing a higher flow resistance than said main channel.
The microfluidic analysis system may further comprise a second weir located upstream from said connected firs end of said side channel, said first and second weirs forming a chamber therebetween, said second weir providing at least one flow gap to allow, in use, at least some fluid to flow past said second weir while trapping said packing material within said chamber.
Each side channel connection to said main channel may be provided with a hook structure whereby, in use, packing material is sprayed into said chamber to facilitate even packing.
Said hook structure preferably at least partially obstructs direct line-of-sight entry of packing material from said side channel into said chamber and forms a chamber mouth to one side of said hook structure.
The present invention also provides a method of packing the chamber in the microfluidic analysis system as claimed above, said method comprising, providing a non-conductive substrate and effecting an electrokinetic flow by applying a relatively high voltage at said reservoir, said reservoir containing packing material, and providing relatively low voltages at said first and second ends of said main channel, whereby, packing material flows from said reservoir into said chamber and is trapped by said first and second weirs.